From 222323eaa0cdb7e6a96f0db14df806d1ad9c5bf0 Mon Sep 17 00:00:00 2001
From: Graham <gpe@openrs2.dev>
Date: Sat, 8 Aug 2020 11:22:03 +0100
Subject: [PATCH] Add AssignExpr support to IdentityTransformer

It can now simplify expressions like `x += 0`.

Signed-off-by: Graham <gpe@openrs2.dev>
---
 .../deob/ast/transform/IdentityTransformer.kt | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt b/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt
index a57d96c4..979b29d1 100644
--- a/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt
+++ b/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt
@@ -1,11 +1,13 @@
 package dev.openrs2.deob.ast.transform
 
 import com.github.javaparser.ast.CompilationUnit
+import com.github.javaparser.ast.expr.AssignExpr
 import com.github.javaparser.ast.expr.BinaryExpr
 import com.github.javaparser.ast.expr.Expression
 import com.github.javaparser.ast.expr.IntegerLiteralExpr
 import com.github.javaparser.ast.expr.LongLiteralExpr
 import com.github.javaparser.ast.expr.UnaryExpr
+import com.github.javaparser.ast.stmt.ExpressionStmt
 import dev.openrs2.deob.ast.Library
 import dev.openrs2.deob.ast.LibraryGroup
 import dev.openrs2.deob.ast.util.walk
@@ -46,6 +48,28 @@ class IdentityTransformer : Transformer() {
                 }
             }
         }
+
+        unit.walk { expr: AssignExpr ->
+            val identity = when (expr.operator) {
+                // x += 0, x -= 0
+                AssignExpr.Operator.PLUS, AssignExpr.Operator.MINUS -> expr.value.isZero()
+                // x *= 1, x /= 1
+                AssignExpr.Operator.MULTIPLY, AssignExpr.Operator.DIVIDE -> expr.value.isOne()
+                else -> false
+            }
+
+            if (!identity) {
+                return@walk
+            }
+
+            expr.parentNode.ifPresent { parent ->
+                if (parent is ExpressionStmt) {
+                    parent.remove()
+                } else {
+                    expr.replace(expr.target.clone())
+                }
+            }
+        }
     }
 
     private fun Expression.isZero(): Boolean {